Program for all operations on Circular Linked List in C

In a Circular linked list, every element has a link to its next element in the sequence, and the last element has a link to the first element. A circular linked list is similar to the singly linked list except that the last node points to the first node. Below is the image to illustrate the same:

1. Insertion at the beginning: 

Insert a new node as the first node. The next pointer of last will point to this node and this new node will point to the previous first node.

Below is the implementation of the above operation:

C

// C program for the above operation
#include <stdio.h>
#include <stdlib.h>

// Structure of a linked list node
struct node {
    int info;
    struct node* next;
};

// Pointer to last node in the list
struct node* last = NULL;

// Function to insert a node in the
// starting of the list
void insertAtFront(int data)
{
    // Initialize a new node
    struct node* temp;
    temp = (struct node*)malloc(sizeof(struct node));

    // If the new node is the only
    // node in the list
    if (last == NULL) {
        temp->info = data;
        temp->next = temp;
        last = temp;
    }

    // Else last node contains the
    // reference of the new node and
    // new node contains the reference
    // of the previous first node
    else {
        temp->info = data;
        temp->next = last->next;

        // last node now has reference
        // of the new node temp
        last->next = temp;
    }
}

// Function to print the list
void viewList()
{
    // If list is empty
    if (last == NULL)
        printf("\nList is empty\n");

    // Else print the list
    else {
        struct node* temp;
        temp = last->next;

        // While first node is not
        // reached again, print,
        // since the list is circular
        do {
            printf("\nData = %d", temp->info);
            temp = temp->next;
        } while (temp != last->next);
    }
}

// Driver Code
int main()
{
    // Function Call
    insertAtFront(10);
    insertAtFront(20);
    insertAtFront(30);

    // Print list
    viewList();

    return 0;
}

Output

Data = 30
Data = 20
Data = 10

The time complexity of the insertAtFront function is O(1) as it performs a constant amount of work to insert a node at the front of the linked list.

The time complexity of the viewList function is O(n) as it has to traverse the entire linked list to print its elements.

2. Insertion at the end: 

Inserting a new node as the last node. The next pointer of last will point to this node and this new node will point to the first node.

Below is the implementation of the above operation:

C

// C program for the above operation
#include <stdio.h>
#include <stdlib.h>

// Structure of a linked list node
struct node {
    int info;
    struct node* next;
};

// Pointer to last node in the list
struct node* last = NULL;

// Function to add a new node at the
// end of the list
void addatlast(int data)
{
    // Initialize a new node
    struct node* temp;
    temp = (struct node*)malloc(sizeof(struct node));

    // If the new node is the
    // only node in the list
    if (last == NULL) {
        temp->info = data;
        temp->next = temp;
        last = temp;
    }

    // Else the new node will be the
    // last node and will contain
    // the reference of head node
    else {
        temp->info = data;
        temp->next = last->next;
        last->next = temp;
        last = temp;
    }
}

// Function to print the list
void viewList()
{
    // If list is empty
    if (last == NULL)
        printf("\nList is empty\n");

    // Else print the list
    else {
        struct node* temp;
        temp = last->next;
        do {
            printf("\nData = %d", temp->info);
            temp = temp->next;
        } while (temp != last->next);
    }
}

// Driver Code
int main()
{
    // Function Call
    addatlast(10);
    addatlast(20);
    addatlast(30);

    // Print list
    viewList();

    return 0;
}

Output

Data = 10
Data = 20
Data = 30

3. Insertion after a specific element:

Below is the program to insert a node after a specified node in the linked list:

C

// C program for the above operation

#include <stdio.h>
#include <stdlib.h>

// Structure of a linked list node
struct node {
    int info;
    struct node* next;
};

// Pointer to last node in list
struct node* last = NULL;

// Function to add a new node
// at the end of the list
void addatlast()
{
    // Stores number to be inserted
    int data;

    // Initialize a new node
    struct node* temp;
    temp = (struct node*)malloc(sizeof(struct node));

    // Input data
    printf("\nEnter data to be inserted : \n");
    scanf("%d", &data);

    // If the new node is the
    // only node in the list
    if (last == NULL) {
        temp->info = data;
        temp->next = temp;
        last = temp;
    }

    // Else the new node will be the
    // last node and will contain
    // the reference of head node
    else {
        temp->info = data;
        temp->next = last->next;
        last->next = temp;
        last = temp;
    }
}

// Function to insert after any
// specified element
void insertafter()
{
    // Stores data and element after
    // which new node is to be inserted
    int data, value;

    // Initialize a new node
    struct node *temp, *n;

    // Input data
    printf("\nEnter number after which"
           " you want to enter number: \n");
    scanf("%d", &value);
    temp = last->next;

    do {

        // Element after which node is
        // to be inserted is found
        if (temp->info == value) {
            n = (struct node*)malloc(sizeof(struct node));

            // Input Data
            printf("\nEnter data to be"
                   " inserted : \n");
            scanf("%d", &data);
            n->info = data;
            n->next = temp->next;
            temp->next = n;

            // If temp is the last node
            // so now n will become the
            // last node
            if (temp == last)
                last = n;
            break;
        }
        else
            temp = temp->next;
    } while (temp != last->next);
}

// Function to print the list
void viewList()
{
    // If list is empty
    if (last == NULL)
        printf("\nList is empty\n");

    // Else print the list
    else {
        struct node* temp;
        temp = last->next;
        do {
            printf("\nData = %d", temp->info);
            temp = temp->next;
        } while (temp != last->next);
    }
}

// Driver Code
int main()
{
    // Initialize the list
    addatlast();
    addatlast();
    addatlast();

    // Function Call
    insertafter();

    // Print list
    viewList();

    return 0;
}

Output:

4. Delete the first element: 

Deleting the first node of the linked list. For this, the next pointer of the last will point to the second node of the linked list.  

Below is the implementation of the above operation:

C

// C program for the above operation
#include <stdio.h>
#include <stdlib.h>

// Structure of a linked list node
struct node {
    int info;
    struct node* next;
};

// Pointer to last node in list
struct node* last = NULL;

// Function to add a new node
// at the end of the list
void addatlast(int data)
{
    // Initialize a new node
    struct node* temp;
    temp = (struct node*)malloc(sizeof(struct node));

    // If the new node is the only
    // node in the list
    if (last == NULL) {
        temp->info = data;
        temp->next = temp;
        last = temp;
    }

    // Else the new node will be the
    // last node and will contain
    // the reference of head node
    else {
        temp->info = data;
        temp->next = last->next;
        last->next = temp;
        last = temp;
    }
}

// Function to delete the first
// element of the list
void deletefirst()
{
    struct node* temp;

    // If list is empty
    if (last == NULL)
        printf("\nList is empty.\n");

    // Else last node now contains
    // reference of the second node
    // in the list because the
    // list is circular
    else {
        temp = last->next;
        last->next = temp->next;
        free(temp);
    }
}

// Function to print the list
void viewList()
{
    // If list is empty
    if (last == NULL)
        printf("\nList is empty\n");

    // Else print the list
    else {
        struct node* temp;
        temp = last->next;
        do {
            printf("\nData = %d", temp->info);
            temp = temp->next;
        } while (temp != last->next);
    }
}

// Driver Code
int main()
{
    // Initialize the list
    addatlast(10);
    addatlast(20);
    addatlast(30);

    printf("Before deletion:\n");
    viewList();

    // Function Call
    deletefirst();

    // Print list
    printf("\n\nAfter deletion:\n");
    viewList();

    return 0;
}

Output

Before deletion:

Data = 10
Data = 20
Data = 30

After deletion:

Data = 20
Data = 30

5. Delete the last element: 

Deleting the last node of the linked list. For this, the second last node will point to the first node of the list.

Below is the implementation of the above operation:

C

// C program for the above operation
#include <stdio.h>
#include <stdlib.h>

// Structure of a linked list node
struct node {
    int info;
    struct node* next;
};

// Pointer to last node in list
struct node* last = NULL;

// Function to add a new node
// at the end of the list
void addatlast(int data)
{
    // Initialize a new node
    struct node* temp;
    temp = (struct node*)malloc(sizeof(struct node));

    // If the new node is the only
    // node in the list
    if (last == NULL) {
        temp->info = data;
        temp->next = temp;
        last = temp;
    }

    // Else the new node will be
    // last node and will contain
    // the reference of head node
    else {
        temp->info = data;
        temp->next = last->next;
        last->next = temp;
        last = temp;
    }
}

// Function to delete the last node
// in the list
void deletelast()
{
    struct node* temp;

    // If list is empty
    if (last == NULL)
        printf("\nList is empty.\n");

    temp = last->next;

    // Traverse the list till
    // the second last node
    while (temp->next != last)
        temp = temp->next;

    // Second last node now contains
    // the reference of the first
    // node in the list
    temp->next = last->next;
    last = temp;
}

// Function to print the list
void viewList()
{
    // If list is empty
    if (last == NULL)
        printf("\nList is empty\n");

    // Else print the list
    else {
        struct node* temp;
        temp = last->next;
        do {
            printf("\nData = %d", temp->info);
            temp = temp->next;
        } while (temp != last->next);
    }
}

// Driver Code
int main()
{
    // Initialize the list
    addatlast(10);
    addatlast(20);
    addatlast(30);

    printf("Before Deletion:\n");
    viewList();

    // Function Call
    deletelast();

    // Print the list
    printf("\n\nAfter Deletion:\n");
    viewList();

    return 0;
}

Output

Before Deletion:

Data = 10
Data = 20
Data = 30

After Deletion:

Data = 10
Data = 20

6. Delete at a given position: 

Delete an element from a specified position in the linked list

Below is the implementation of the above operation:

C

// C program for the above operation
#include <stdio.h>
#include <stdlib.h>

// Structure of a linked list node
struct node {
    int info;
    struct node* next;
};

// Pointer to last node in list
struct node* last = NULL;

// Function to add a new node
// at the end of the list
void addatlast()
{
    // Stores number to be inserted
    int data;

    // Initialize a new node
    struct node* temp;
    temp = (struct node*)malloc(sizeof(struct node));

    // Input data
    printf("\nEnter data to be inserted : \n");
    scanf("%d", &data);

    // If the new node is the
    // only node in the list
    if (last == NULL) {
        temp->info = data;
        temp->next = temp;
        last = temp;
    }

    // Else the new node will be
    // last node and will contain
    // the reference of head node
    else {
        temp->info = data;
        temp->next = last->next;
        last->next = temp;
        last = temp;
    }
}

// Function to delete an element
// at a specified index in the list
void deleteAtIndex()
{
    // Stores the index at which
    // the element is to be deleted
    int pos, i = 1;
    struct node *temp, *position;
    temp = last->next;

    // If list is empty
    if (last == NULL)
        printf("\nList is empty.\n");

    // Else
    else {

        // Input Data
        printf("\nEnter index : ");
        scanf("%d", &pos);

        // Traverse till the node to
        // be deleted is reached
        while (i <= pos - 1) {
            temp = temp->next;
            i++;
        }

        // After the loop ends, temp
        // points at a node just before
        // the node to be deleted

        // Reassigning links
        position = temp->next;
        temp->next = position->next;

        free(position);
    }
}

// Function to print the list
void viewList()
{
    // If list is empty
    if (last == NULL)
        printf("\nList is empty\n");

    // Else print the list
    else {
        struct node* temp;
        temp = last->next;
        do {
            printf("\nData = %d", temp->info);
            temp = temp->next;
        } while (temp != last->next);
    }
}

// Driver Code
int main()
{
    // Initialize the list
    addatlast();
    addatlast();
    addatlast();

    // Function Call
    deleteAtIndex();

    // Print the list
    viewList();

    return 0;
}

Output: